Variable resistance pickup element



March 20, 1951 5, u KE 2,545,737

VARIABLE RESISTANCE PICKUP ELEMENT Filed Nov. 1, 1947 Ina F2 Zaa. ZZZEEL/izz E -Luke I7 7 A fl ig;

Patented Mar. 20, 1951 VARIABLE RESISTANCE PICKUP ELEMENT Marvin B. Luke, Akron, Ohio, assignor to The B. F. Goodrich Company, New York, N. Y., a corporation of New York Application November 1, 1947, Serial N 0. 783,461

8 Claims.

This invention relates to pick-up elements for converting mechanical energy into electrical energy and is useful especially in translating vibratory movements of a needle in the grooves of a phonograph record into variations in the electrical energy of an amplifying circuit.

Objects of the invention are to provide an improved pick-up element of resilient rubber containing an electrically conductive substance and in which the electrical resistance is varied by mechanically distorting the rubber preferably by stretching and relaxing the same, to provide an improved construction of the element effective for the purpose, to provide an element of improved electrical and mechanical properties, especially with reference to the surface condition an internal character of the element and the current conducting connection, to provide for obtaining uniformly high quality in production, to provide improved frequency response over a wide range, and to provide for convenience in manufacture and installation.

These and further objects will be apparent from the following description, reference being had to the drawings in which:

Fig. l is a plan view partly in section of a pick-up element constructed in accordance with and embodying the invention.

Fig. 2 is a plan View of a pick-up element installed in a phonograph pick-up head.

Fig. 3 is a section taken along line 3-3 in Fig. 2.

Fig. 4 is a diagrammatic view of an example of amplifying circuits suitable for use with the pick-up element.

Fig. 5 is a plan view of a modified pick-up head.

Fig. 6 is a section taken along line 65 of Fig. 5.

Fig. 7 is a plan View of a microphone constructed in accordance with and embodying the invention.

Fig. 8 is a section taken along line 8-43 in Fig. '7.

In the pick-up element of the invention, an embodiment of which is show in Fig. 1, a body of resilient rubber or other rubber-like material containing discrete particles of electrically conductive substance such as metallic particles or carbon which may be in the form of graphite particles, acetylene black or carbon black is produced as a full molded article having the shape, internal structure and formed surface characteristics of molded rubber. The pick-up element may be molded to a dumb-bell shape as shown in Fig. 1 comprising enlarged end portions l0, l9 and a central enlarged portion ll joined by smaller neck portions I2, 12 which neck portions merge with the enlarged portions preferably in smooth curves.

Inasmuch as the pick-up element is preferably both mounted and operated in a condition of stretch, the resistance to electric current passing between an end portion I!) and the middle portion H is determined principally by the construction and properties of the neck portion 12 which undergoes the greatest percentage of stretch owing to its reduced cross-section and will have the greatest change in resistance for a given amount of stretch. Thus, the reduced neck portion increases the electrical sensitivity of the pick-up element. In addition to the formation of the material in the neck portions [2, 12 the full molded character provides uniformly smooth surface conditions all of which are important in obtaining the desired electrical response under changes in tension.

It has been found that imperfections in the pick-up element structure are objectionally productive of noises and unreliable operation particularly where minute movements and small electrical currents are involved. The maufacture of the pick-up element as a full molded article has the distinct advantage for the puposes of the invention in that the structure of the pick-up element and the desired surface conditions, which are of critical importance in the electrical results produced, may readily be obtained with a high degree of uniformity of quality when the elements are produced in quantity.

The dimensions of the body of the element particularly in the neck portions [2, l2 may be suited in relation to the resistance of the material, the amplitude of the mechanical movement, and such factors as the voltage impressed to produce the desired results in accordance with the mechanical and electrical equipment with which the pick-up element is used.

The molded construction moreover makes possible improved attachment of connectors l3, 13 both electrically and mechanically. It will be seen Where an element is mounted under tension that the attachment and proper electrical conductivity must be provided through the interface or region of attachment of the connectors to the body of rubber-like material. It is found that these requirements can be conveniently and effectively carried out by the full molded construction in which the body of rubber-like material is preferably bonded directly to the metal 3 of the connectors I3, It with or without aid of a suitable adhesive, by vulcanization in the molding operation. The portions of the connectors I3, 43 which are embedded in the body of the element may be enlarged as at heads I4, I4 to provide larger surfaces for increased conductivity and strengthof connection.

As an example of applications in which the pick-up element may be advantageously utilized, Figs. 2, 3 and 4 show a suitable pick-up head and manner of attachment to an electrical circuit. The pick-up head may comprise a housing I5 of electrically non-conductive material in which the pick-up element may be mounted as shown in Fig. 2. The connectors I3, I3 are supported in the housing l5 and may be secured to the housing by set screws I6, I6 to facilitate mounting the pick-up element under tension. The middle connector I3 is, mounted on a pinion member ll journalled in thehousing- -I5;andhas a "suitable bearing such as a resilient rubber sleeve l8 which is mounted around the .pinion and on the housing. A-needle i9 is mounted on the pinion I l and its shank extends radially outward from the pinion to provide leverage for turnin the pinion, and stretching the bodyofresilient rubber-like material.

The pick-up housing it; has terminals 26, 22 and 23 which are connected to anamplifying circuit shown in Fig. A-b-yleads 24, 25 and .26. The terminals are .alsoelectrically connected through flexible leads 27, .28-and 29 to the connectors 53, I3 of the pick-up element. Inthe circuita voltage is impressed across the pick-up element .between the end connectors I3, 13 and theresistance of the element to the flow of current sets up a difference .in potential betweenthe connectors whichis varied .by movementof the needle to provide a varying input voltage to the am plifier.

The amplifyingcircuit'comprises an input circuit 3i which includes leads .25, 25 the .corresponding half of the pick-up element, and the grid circuit of an amplifying tube 32. Output circuit 33 may be connected to other circuits ,for converting voltage variations into soundenergy.

The pick-up element of the electrically conductive rubber material has a property whereby its resistance to current flow decreases gradually as the pick-up .is stressed in tension. "This property is utilized in the operation of the pickup element upon lateral movement of the needle I9 .such as may be caused bythe grooves of phonographrecords. Lateral movement of the middle connector i3 .is produced which varies the tension in thepick-up element and thisis accompanied by a variation in the resistance. The pick-up element is preferably mounted under tension. so that lateral movement of the middle connectorl3 increases or reduces the tension in the portions I2, 12 of the pick-up element between the middle and end connectors I13, 53 in accordance with the movement of theneedle I9.

A modified pick-up head accommodating two of the pick-up elements is shown in-Fig. 5. The housing 34 which may be composed of electrically non-conductive material is constructed 'in a manner such thatthe two pick-up elements may be mounted therein. Each elementmay be of the construction of Fig. 1 and in this case mounted around a centrally located pinion I l which is mounted in the housing 34. The middle connectors I3, I3 are'both secured as by soldering to the pinion while the end connectors I3, 13 are secured adjustably in the housing 34 by set screws 35, 35 for mounting the pick-up elements under tension. A needle 36 mounted on the pinion I1 is adapted to engage the grooves of a phonograph record and upon actuation by the variations in the grooves moves the pinion thereby causing corresponding variations in tensioninboth of the pick-up elements with the accompanying variations in resistance.

The pick-up head has terminals 3?, 3? which are connected to one end connector of the pickup element by leads 38, 38. The terminals 37, 3"! may be connected to an amplifying circuit and the resistance of the-upper portion of the lefthand pick-up element and the lower portion of the .righthand pick-up element as shown in Fig.

5 act as resistances in series in the input circuit of the amplifying circuit. In this arrangement connected as shown only two terminals are required. The voltage connection and the grid input terminal may be combined .as one with the other. serving as ground.

The pick-up element of the invention may be used to convert sound vibrations into electrical impulses in apparatus such as the microphone shown in Figs. 7 and 8. A cup-shaped microphone housing 40 of electrically non-conducting material has posts 4!, 4i mounted therein which have apertures for receiving the end connectors 93, I3 of a pick-up element. Set screws 42, 42 in the posts ll, ll may be used to securethe pickup element in tension. A middle connector I3 or the elementis connected to, a pinion I? which is journaled in the microphone housing) in a manner such that rotation of'the pinion Ii moves the middle connector I3 and causes variation in the "tension'of the portions or" the pick-up ele ment.

The microphone housing an has a diaphragm i3'of suitable material such as metal or 'fiber disposed across the open end which is clamped between the housing and a flanged collar =34. An arm 45 is mounted on the diaphragm 43 and on the pinion I! in a manner such that vibration of-the diaphragm caused by sound to which it is exposed causes the arm and-pinion to turn. The turning "of the pinion 'll causes variations in the tension of the pick-up element and produces variations in the resistance of the element. Leads 46, 47 and 48 of an amplifying circuit are secured to the connectors I3, l3 and thevariations in resistance in the pick-up element produce variations in the current of the circuit in accordance with the vibrations of the diaphragm "for translating the sound energy into electrical energy.

Variations may be made Without departing from the scope of the invention'as it is described in the following claims.

I claim:

1. A pick-up element for producing electrical variations in response to mechanical movement, said element comprising a body of resilient rubber-like material containing an electrically conductive substance and including means-for mounting said body in a condition of tension, said mounting means comprisingrelat'ively movable connectors secured to said body at spaced apart positions to stretch and relax portions of said body between said positions undersaid movement to vary the conductivity thereof, said body being full molded in a dumb-bell shape with the enlarged portions of the dumb-bell at the ends and middle thereof and presenting in the intermediate, reduced portions of the dumb-bell unrestrained moldedsurfaces subject to the stretching and relaxing 'movementapplied at said enlarged portions, said intermediate reduced portions of the body being unrestrained and composed of said rubber-like material containing said conductive substance throughout the region of said reduced portions, and said enlarged portions having openings therein and said connectors having enlarged portions disposed in said openings and secured to the body material by a union of vulcanization.

2. A pick-up element for producing electrical variations in response to mechanical movement, said element comprising a body of resilient rubber-like material containing an electrically conductive substance and including means for mounting said body at opposite end portions in a condition of stretch and for applying movement to the midportion of the body for varying the tension in said body and thereby the conductivity thereof, said means comprising connectors secured to said end portions and to said midportion by a union of vulcanization, said body being generally circular in cross section and having unrestrained necked portions of reduced crosssection between said midportion and said end portions composed of said rubber-like material containing said conductive substance throughout the region of said necked portions and said necked portions having unrestrained uniformly smooth, molded surfaces subject to the variations in tension under said movement.

3. An element for producing electrical variations in response to mechanical movement, said element comprising a body of resilient rubber-like material containing an electrically conductive substance and including means for mounting said body to maintain it in a condition of tension and to vary the tension therein and thereby vary the conductivity thereof, said body having an unrestrained full-molded surface subject to the variations in tension and having openings in the body at spaced-apart positions, and said means comprising connectors in said openings and secured to said body.

4. An element for producing electrical variations in response to mechanical movement, said element comprising a body of resilient rubber-like material containing an electrically conductive substance and including means for mounting said body at opposite end portions for maintaining said body in a stretched condition and for applying said movement to the midportion of said body for varying the tension in said body, said body having a smooth full-molded surface subject to the variations in tension and having openings in said end portions and midportion, and said means comprising members disposed in said openings and secured to said material by a union of vulcanization.

5. An element for producing electrical variations in response to mechanical movement, said element comprising a body of resilient rubberlike material containing an electrically conductive substance and including means for mounting said element at spaced-apart positions along the same, said means comprising relatively movable connectors embedded in and secured to said body at said positions to stretch and relax the portion of said body between said positions under said movement and thereby vary the conductivity of said portion, said portion between said positions being necked to a reduced cross-section for increased stretchability in the region of the necked portion and increased electrical sensitivity in said region as compared with the portions of said body nearer said positions and said necked portion being unrestrained and composed of full-molded rubber-like material containing saidconductive substance entirely through the cross section throughout the region of the necked portion.

6. An element for producing electrical variations in response to mechanical movement, said element comprising a body of resilient rubberlike material containing an electrically conductive substance and including means for mounting said element at spaced-apart positions along the same, said means comprising relatively movable connectors embedded in and secured to said body at said positions to stretch and relax the portion of said body between said positions under said movement and thereby vary the conductivity of said portion, said portion between said positions being necked to a reduced cross-section for increased stretchability in the region of the necked portion and increased electrical sensitivity in said region as compared with the portions of said body nearer said positions and said necked portion being composed of full-molded rubber-like material containing said conductive substance throughout the region of the necked portion subject to the stretching and relaxing action.

7. A pick-up element for producing electrical variations in response to mechanical movement, said element comprising a body of resilient rubber-like material containing an electrically conductive substance full-molded in a dumb-bell shape with enlarged portions at the ends and middle thereof providing intermediate reduced portions therebetween, a pair of relatively movable end connectors embedded in and secured to said enlarged end portions for mounting said body under tension and a middle connector embedded in and secured to the middle enlarged portion for changing the amount of stretch in the intermediate reduced portions between said end connectors and said middle connector.

8. A pick-up element for producing electrical variations in response to mechanical movement, said element comprising a body of resilient rubber-like material containing an electrically conductive substance full-molded in a dumb-bell shape with enlarged portions at the ends and middle thereof providing intermediate reduced portions therebetween of generally round crosssection, said reduced portions being composed of said rubber-like material containing said conductive substance throughout the region of said reduced portions, and connectors having enlarged portions embedded in said enlarged portions of said body and secured thereto by a union of vulcanization.

MARVIN B. LUKE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,037,255 Miller Apr. 14, 1936 2,047,094 Bennett July 7, 1936 2,136,848 Hassler Nov. 18, 1938 2,305,717 LaBell Dec. 22, 1942 2,429,137 Root Oct. 14, 1947 2,451,992 Grotenhuis Oct. 19, 1948 2,471,601 Albright May 31, 1949 2,472,214 Hurvitz June 7, 1949 2,491,794 Bachman Dec. 20, 1949 

